The genus Thiobacillus consists of colorless rod-shaped bacteria that are gram-negative (a classification test based on differences in bacterial cell walls). They prefer temperatures between 77 degrees and 95 degrees Fahrenheit. Most species of Thiobacilli are aerobic (require oxygen to respire), though some are considered facultative anaerobes (can respire with or without oxygen). They require inorganic sources to grow and contain an enzyme called ferrous oxidase that allows them to metabolize iron.
Well Water Systems
Thiobacilli often contaminate well water systems, producing a rotten egg odor due to production of sulfuric compounds. They also turn pipes black and produce a thick slime, called a biofilm. This biofilm contains sulfuric acid, which erodes the well casing, pumps and pipes. Contamination of wells is more common in the Southeast, where high temperatures provide the heat-loving conditions favored by Thiobacilli. Poorly-maintained filtration systems encourage its growth.
According to RealTime Laboratories, Thiobacillus ferrooxidans was the major source of sulfur-reducing bacteria isolated from Chinese drywall. The sulfuric acid produced by Thiobacilli is a significant source of pollution. During the construction boom between 2002 and 2005, drywall from China that was contaminated with this bacterium was imported into the United States. The bacteria were present in gypsum from coal mines in China.
Thiobacillus concretivorous has been found in wastewater treatment plants. It is named for its ability to “eat concrete” by consuming the polythionates in waste and producing sulfuric acid. Additional contaminants unrelated to Thiobacilli presence, such as molds, yeast, and other types of bacteria, also accelerate the decomposition of concrete. Thiobacillus thiooxidans has been implicated in the decomposition of concrete sewer pipes, aided by the presence of gypsum and low pH. Thiobacilli can corrode the pipes leading into households, contaminating the water supply.
Benefits of Thiobacillus
Thiobacillus dentrificans is named for its ability to reduce nitrates to nitrites under anaerobic (without oxygen) or aerobic (with oxygen) conditions and is used for bioremediation purposes. This bacterium is classified as a chemoautolithotroph, meaning that it derives its carbon from carbon dioxide and uses inorganic compounds such as iron or sulfur for growth. Nitrates contaminate groundwater. This bacterium reduces nitrates to nitrites, often using pyrite or other sulfur minerals as an inorganic source of electrons in the chemical process.